Fuse for use in a semiconductor device, and semiconductor devices including the fuse

ABSTRACT

A metal silicide fuse for a semiconductor device. The fuse includes a conductive region positioned adjacent a common well of a first conductivity type, a terminal region positioned adjacent a well of a second conductivity type, and a narrowed region located between the terminal region and the conductive region and positioned adjacent a boundary between the two wells. Upon applying at least a programming current to the fuse, the fuse “blows” at the narrowed region. The diode or diodes between wells of different conductivity types wells and the Schottky diode or diodes between the remaining portions of the fuse and wells adjacent thereto control the flow of current through the remainder of the fuse and through the associated wells of the semiconductor device. When the fuse has been “blown,” the diodes and Schottky diodes prevent current of a normal operating voltage from flowing through the wells of the semiconductor device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/943,993, filed Aug. 30, 2001, pending, which is a continuation ofapplication Ser. No. 09/293,192, filed Apr. 16, 1999, now U.S. Pat. No.6,323,534, issued Nov. 27, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to the design andfabrication of semiconductor devices. Specifically, the presentinvention relates to a fuse for use in a semiconductor device, tomethods of fabricating the fuse, and to a semiconductor device thatincludes the fuse. In particular, the present invention relates to asilicide fuse of a semiconductor device and to a semiconductor memorydevice that includes the silicide fuse. More particularly, the presentinvention relates to a semiconductor device that includes two diffusionregions disposed substantially within a well of opposite conductivitytype, each of which communicates with an end of a metal silicide fuse.

[0004] 2. Background of Related Art

[0005] Computers typically include devices that store data, such asmemory devices. A first type of memory device is referred to as a readonly memory (“ROM”) device, in which data is permanently stored andcannot be overwritten or otherwise altered. Thus, ROM devices are usefulwhenever unalterable data or instructions are required. ROM devices arealso nonvolatile devices, meaning that the data is not destroyed whenpower to these devices is shut off. ROM devices are typically programmedduring their fabrication by making permanent electrical connections inselected portions of the memory device. One disadvantage of ROM devicesis that their programming is permanently determined during fabricationand cannot, therefore, be changed. Thus, when new programming isdesired, a ROM device must be newly configured to be wired in accordancewith the desired program.

[0006] Another type of memory device is a programmable read only memory(“PROM”) device. Unlike ROM devices, PROM devices may be programmedafter their fabrication. To render PROM devices programmable, some PROMdevices are provided with an electrical connection in the form of afusible link, which is also typically referred to as a fuse. Aconsiderable number of fuse designs are known and employed in PROMdevices. Exemplary fuse designs are disclosed in PROM Fuse Design Scalesto Sub0.25 Micron, Electronic Engineering Times, Sep. 29, 1997, p.4, inIEEE Transactions on Electron Devices, Vol. 33, No. 2, p.250-253(February 1986), and in U.S. Pat. Nos. 5,672,905, 4,679,310, 5,264,725,4,935,801, 4,670,970, 4,135,295, and 4,647,340.

[0007] An exemplary use of fuses in semiconductor devices has been inredundancy technology. Redundancy technology improves the fabricationyield of high-density semiconductor devices, such as static randomaccess memory (“SRAM”) devices and dynamic random access memory (“DRAM”)devices, by facilitating the substitution of a redundant program circuitfor a failed program circuit that could otherwise render thesemiconductor device useless. The failed circuit may be bypassed and theredundant circuit activated or programmed by selectively programming, or“blowing,”, fuses of the semiconductor device.

[0008] Fuses are perhaps the simplest and most compact means ofprogramming a semiconductor memory device with a particular wiringscheme. Perhaps the most common fuse design is a conductive layer,typically comprising metal or polysilicon, which is narrowed or “neckeddown” in one region. To blow the fuse, a relatively high electricalcurrent, or programming current, is applied to the fuse. The programmingcurrent heats the metal or polysilicon of the fuse to a temperatureabove the melting point of the metal or polysilicon. As the fuse melts,the metal or polysilicon of the fuse “blows” or becomes discontinuous,breaking the conductive link across the fuse. Typically, the fusebecomes discontinuous at the narrowed region since the material volumeat the narrowed region is smaller than that of other portions of thefuse and, consequently, the current density is highest and thetemperature increases most quickly at the narrowed region of the fuse.By selectively “blowing” the fuses of a PROM device, the PROM device isprogrammed to have a desired wiring scheme with conductive andsubstantially nonconductive fuses, thereby imparting each location ofthe PROM with a corresponding value of “1” or “0” representative of theconductivity state of the fuse (i.e., either conductive or substantiallynonconductive), an array of which values comprises the data stored inthe semiconductor device.

[0009] As an alternative to employing an electrical current to program asemiconductor device, a laser may be employed to blow selected fuses.The use of lasers to “blow” fuses has, however, become increasinglydifficult as the size of the features of semiconductor devices,including the fuses thereof, decreases and as the density of features ofsemiconductor devices increases. Since the diameter of a laser beamshould be smaller than the fuse pitch, the utility of laser beams to“blow” fuses begins to diminish with fuse pitches that are about thesame or less than the diameters of conventional (e.g., about 5 microns)and state of the art laser beams.

[0010] As the programming current or laser beam intensity required to“blow” a conventional fuse may damage regions or structures of thesemiconductor device proximate the fuse, conventional fuses are somewhatundesirable. Moreover, if the use of laser beams is desired to programthe fuses of a semiconductor device, the fuse pitch and, thus, thedensity of structures on the semiconductor device may be limited.

[0011] When a metal fuse is disposed adjacent a doped silicon or dopedpolysilicon structure to bridge selected regions thereof, the resistanceof the adjacent silicon or polysilicon may not differ significantly fromthe resistance of the fuse. Thus, upon “blowing” the fuse, the adjacentsilicon or polysilicon may continue to transmit current similar to thecurrent carried across an intact fuse. This is especially problematicwhen such a fuse is disposed adjacent a region, such as an n-well, of asemiconductor substrate conductively doped to have a first conductivitytype to bridge two separate conductive wells, such as p-wells, of asecond conductivity type, opposite the first conductivity type, disposedadjacent the region of first conductivity type. If the fuse “blows” in amanner that leaves a section of a second, or outlet, side of the fusethat overlaps both a p-well and a portion of the common n-well, currentmay continue to pass into a p-well from a first side of the “blown”fuse, into the n-well, and out of the n-well to the portion of thesecond side of the “blown” fuse that overlaps the n-well. Thus, a fusethat blows in such a manner may undesirably conduct current havingsubstantially the same characteristics as current conducted across anintact fuse.

[0012] Moreover, since electrically conductive metal silicide structuresmay be fabricated by annealing metal to an adjacent silicon orpolysilicon structure, metal fuses that are disposed adjacent to siliconor polysilicon structures may conduct current even after being “blown.”This may occur if a high enough current is applied to the fuse or if thefuse is otherwise heated to a sufficient temperature to cause the metalof the fuse to anneal to the adjacent semiconductive material and tothereby form a metal silicide that may bridge the discontinuous portionof the fuse. The “blown” fuse may thus undesirably conduct currenthaving substantially the same characteristics as current conductedacross an intact fuse.

[0013] Accordingly, there is a need for a fuse that may be fabricatedadjacent a semiconductive region of a state of the art semiconductordevice and that, upon programming, or “blowing,” the fuse has asignificantly different resistance than the previously intact fuse.There is also a need for a fuse that can be fabricated by knownsemiconductor device fabrication techniques.

BRIEF SUMMARY OF THE INVENTION

[0014] The present invention generally provides a fuse for integratedcircuits and semiconductors. The fuse of the present invention comprisesa metal silicide layer with at least one terminal end thereof contactingan area of a semiconductor substrate that has been implanted with adopant of a second conductivity type. A conductive region of the fuse,which is disposed adjacent the at least one terminal end, contactsanother area of the semiconductor substrate that has been implanted witha dopant of a first conductivity type. The at least one terminal end andthe conductive region of an intact fuse according to the presentinvention are joined by a narrowed region disposed over a boundarybetween the areas of first and second conductivity types. Whensufficient current flows through the fuse, the metal silicide layermelts, agglomerates, or “balls up,” or otherwise ceases to conductelectrical current along the substantial length thereof, which resultsin an open circuit. This agglomeration preferably occurs at the narrowedregion of the fuse.

[0015] Another embodiment of the semiconductor device and the fusethereof includes a semiconductor substrate with two separate wells of asecond conductivity type, preferably p-type, disposed in thesemiconductor substrate, a common well of a first conductivity type,preferably an n-type conductivity, adjacent and disposed between the twoseparate wells, and a substantially flat metal silicide structuredisposed adjacent the semiconductor substrate, with terminal ends of themetal silicide structure in communication with the two separate wellsand a central, or conductive, region of the metal suicide structuredisposed adjacent the common well. The semiconductor substrate maycomprise p-type silicon. The common well is preferably a lightly dopedregion of the semiconductor substrate. The two separate wells comprisesemiconductor material of a second conductivity type, which is oppositethe first conductivity type, and are located within the common well andadjacent a surface of the substrate. The two separate wells arepreferably highly doped.

[0016] The metal silicide of the fuse may comprise titanium silicide,tantalum silicide, tungsten silicide, molybdenum silicide, cobaltsilicide, lead silicide, nickel silicide, platinum silicide, or anyother metal silicide. Preferably, the metal silicide of the fusecomprises a refractory metal silicide. The metal silicide layer mayinclude a necked down region, or narrowed region, which is preferablynarrower in width and has a smaller volume of conductive material thanthe terminal ends of the fuse, located between a terminal end throughwhich current exits the fuse and the central region of the fuse.

[0017] Preferably, the narrowed region is disposed adjacent theinterface between a second well of the two separate wells and the commonwell. Accordingly, as a programming current is applied to the fuse, thefuse will preferably become discontinuous adjacent the interface betweenthe second well and the common well. Thus, a first remaining portion ofthe fuse will lie adjacent a first well of the two separate wells andthe region of the n-well adjacent thereto, while a second portion of thediscontinuous fuse will lie adjacent only the second well of the twoseparate wells. After the fuse has been blown, as current is applied tothe fuse, the current will pass into the first of the two separate wellsand, thus, into the common well through the first portion of the “blown”fuse. A diode, which exists at the interface between the second well ofthe two separate wells and the common well, which interface is alsoreferred to as a p-n junction, as a depletion zone, as a boundary, or asa border, prevents electrical current from entering the second of thetwo separate wells through the common well. Accordingly, as the fuse isopen, “blown,” or otherwise becomes discontinuous at the narrowed regionthereof, the fuse will no longer conduct a significant amount of currentand, therefore, an open circuit is created.

[0018] Since the fuse material comprises metal suicide, the fuse of thepresent invention inhibits reconnection of the fuse by growth of a metalsilicide layer and, therefore, re-closing of the circuit is prevented.

[0019] The present invention also includes a method of fabricating afuse and a semiconductor device according to the present invention.Preferably, the fuse is fabricated on a semiconductor substrate thatincludes two separate wells of a second conductivity type disposedwithin a lightly doped region, or common well, of a first, oppositeconductivity type. A metal silicide structure may be fabricated on thesubstrate such that terminal ends of the fuse communicate with the twoseparate wells and a central portion of the metal silicide structure isadjacent the common well.

[0020] The semiconductor substrate may be a p-type silicon wafer.Accordingly, the method may include lightly doping a desired diffusionregion of the substrate to impart the desired location of the commonwell with a first conductivity type (e.g., n-type) that is opposite thelight, p-type conductivity of the semiconductor substrate. The lightlydoped common well may be formed by implanting ions of the firstconductivity type to a first concentration into selected portions of thesemiconductor substrate. The desired locations of the two separate wellsthat are to be disposed adjacent or within the lightly doped common wellmay be doped to have an opposite conductivity type (e.g., p-type) thanthe common well. The two separate wells may be highly doped and may beformed by implanting ions of the opposite conductivity type to a secondconcentration, which is preferably higher than the first concentration.

[0021] The metal silicide structure may be fabricated by disposing alayer of metal, such as titanium, tantalum, tungsten, molybdenum,cobalt, lead, or platinum adjacent at least the common well and the twoseparate wells of the semiconductor substrate. A layer of silicon mayalso be disposed adjacent the layer of metal, if necessary, to fabricatea metal silicide structure of the desired configurations and dimensions.The layer of metal and the layer of silicon, if any, may be patterned tosubstantially the desired configuration of the metal silicide fuse.Preferably, the metal and silicon layers are patterned to define a fusestructure including a narrow, elongated conductive region, a narrowedregion adjacent an end of the conductive region, and at least oneterminal end that is wider than the narrowed region and disposedadjacent the narrowed region, opposite the conductive region.Alternatively, the fuse may be defined after a metal silicide layer hasbeen formed. The layer of metal may be heated to anneal or otherwisereact the metal with the silicon of either the substrate or an adjacentlayer of silicon to form the metal silicide structure. Alternatively, alayer of metal silicide may be disposed adjacent the semiconductorsubstrate by other known processes, such as by chemical vapor deposition(“CVD”) techniques, then patterned to define the fuse.

[0022] Other features and advantages of the present invention willbecome apparent to those of ordinary skill in the art through aconsideration of the ensuing description, the accompanying drawings, andthe appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0023] The figures presented in conjunction with this description arenot actual views of any particular portion of an actual semiconductordevice or component, but are merely representations employed to clearlyand fully depict the present invention.

[0024]FIG. 1 is a cross-sectional representation of a semiconductordevice including a fuse according to the present invention, which fuseincludes a central, or conductive, region disposed adjacent and incommunication with an n-well of the semiconductor substrate and end, orterminal, regions that are continuous with the conductive region, eachterminal regions of which is disposed adjacent and in communication witha p-well disposed within or adjacent to the n-well;

[0025]FIG. 1A is a schematic representation of a top view of thesemiconductor device, including the fuse thereof, of FIG. 1;

[0026]FIG. 1B is a schematic representation of a circuit including thesemiconductor device and the fuse thereof of FIG. 1;

[0027]FIG. 2 is a cross-sectional representation of a semiconductordevice including another embodiment of the fuse of the presentinvention;

[0028]FIG. 3 is a cross-sectional representation of a semiconductordevice including yet another embodiment of the fuse of the presentinvention;

[0029]FIG. 3A is a schematic representation of a circuit including thesemiconductor device and fuse of FIG. 3;

[0030]FIGS. 3B and 3C are schematic representations of the semiconductordevice and circuit of FIGS. 3 and 3A, respectively, illustrating thesemiconductor device and circuit including a “blown” fuse;

[0031]FIG. 4 is a cross-sectional representation of a “blown” fuseaccording to the present invention and, in particular, the fuseillustrated in FIG. 1;

[0032]FIG. 4A is a schematic representation of a circuit of the “blown”fuse of FIG. 4;

[0033]FIG. 5 is a cross-sectional representation of a semiconductordevice including the fuse of the present invention, such as the fuseillustrated in FIG. 1, that has been undesirably resistively “blown”and, therefore, will continue to conduct current;

[0034]FIG. 5A is a schematic representation of a circuit including theresistively “blown” fuse illustrated in FIG. 5;

[0035] FIGS. 6-12 are cross-sectional representations of a semiconductordevice, illustrating an embodiment of a method of forming conductivelydoped wells in the semiconductor substrate and of fabricating fieldisolation regions thereon;

[0036] FIGS. 13-18 are cross-sectional representations of asemiconductor device, illustrating an alternative embodiment of themethod of forming conductively doped wells in the semiconductorsubstrate and of fabricating field isolation regions thereon; and

[0037]FIGS. 19, 19A and 20 are cross-sectional representations of asemiconductor device, illustrating an embodiment of a method offabricating the metal silicide fuse.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The following description provides specific details about thefuse and methods of the present invention in order to provide a thoroughunderstanding of the present invention. The skilled artisan, however,would understand that the present invention may be practiced withoutemploying these specific details. Indeed, the present invention can bepracticed in conjunction with other materials, differently configuredstructures, and other fabrication techniques, such as those known in theindustry.

[0039] The process steps and structures described herein do not form acomplete process flow for fabricating semiconductor devices or acompleted device. Only the process steps and structures necessary tounderstand the present invention are described.

[0040] With reference to FIGS. 1 and 1A, a semiconductor device 10including a fuse 20 according to the present invention is illustrated.Semiconductor device 10 includes a semiconductor substrate 12 withinwhich a common well 14 of a first conductivity type is disposed. Atleast two separate wells 16 and 18 of a second conductivity type, whichis preferably opposite the first conductivity type of common well 14,are disposed within or adjacent common well 14.

[0041] Fuse 20, which is disposed adjacent semiconductor substrate 12,includes terminal regions or ends 22 and 24, which are also referred toherein as second regions, that are disposed adjacent wells 16 and 18,respectively. A conductive central region 26, which is also referred toherein as a central region or as a first region, of fuse 20 is disposedbetween terminal ends 22 and 24 and facilitates communication betweenterminal ends 22 and 24. Central region 26 is disposed adjacent commonwell 14. A narrowed region 28, or necked-down region, of fuse 20 may bedisposed between conductive region 26 and terminal end 24, adjacent theboundary, border, or interface between well 18 and common well 14.Narrowed region 28 preferably has a smaller volume of conductivematerial than terminal ends 22 and 24 and than central region 26.Semiconductor device 10 may also include at least two contacts 30 and 32disposed in communication with terminal ends 22 and 24, respectively.

[0042] Semiconductor substrate 12, which is preferably a p-typesubstrate, may comprise a semiconductor wafer, such as a silicon wafer,or a silicon layer of a silicon on insulator (“SOI”) structure, such asa silicon on glass (“SOG”) structure, a silicon on ceramic (“SOC”)structure, or a silicon on sapphire (“SOS”) structure.

[0043] Common well 14 preferably comprises an n-well. Thus, the firstconductivity type of common well 14 is an n-type conductivity. Asillustrated, common well 14 is disposed adjacent a surface 13 ofsemiconductor substrate 12.

[0044] Wells 16 and 18 are also disposed adjacent surface 13. Wells 16and 18 may be disposed within common well 14 or adjacent thereto. Aswells 16 and 18 comprise semiconductor material doped with a secondconductivity type, which is preferably opposite the first conductivitytype, wells 16 and 18 are preferably p-wells and, therefore, have ap-type conductivity.

[0045] Fuse 20 comprises metal silicide. Exemplary metal silicides thatmay be employed in fuse 20 include, without limitation, titaniumsilicide, tantalum silicide, tungsten silicide, molybdenum silicide,cobalt silicide, lead silicide, and platinum silicide. Preferably, uponthe application of a programming current, the metal silicide of fuse 20agglomerates, or “balls up,” and thereby becomes discontinuous. Suchagglomeration of the metal silicide of fuse 20 may prevent damage toregions of semiconductor device 10 or structures thereof that areproximate fuse 20 as fuse 20 is programmed.

[0046] With continued reference to FIG. 1, as wells 16 and 18 preferablyinclude a high concentration of semiconductor material having a p-typeconductivity and common well 14 preferably includes semiconductormaterial lightly doped to have an n-type conductivity, the p-n junctionsor depletion zones 17 and 19 between well 16 and common well 14 andbetween well 18 and common well 14, respectively, comprise diodes 17′and 19′ (FIG. 1B) that prevent current from flowing into wells 16 and 18from common well 14. The interface between central region 26 of fuse 20and common well 14 comprises a so-called Schottky diode 15′. As is knownin the art, however, at a certain voltage, such as the normal operatingvoltage of semiconductor device 10, Schottky diode 15′ may becomereverse-biased. If Schottky diode 15′ becomes reverse-biased, currentwill flow from common well 14 into central region 26 of fuse 20.

[0047]FIG. 1B is a schematic representation of a circuit 10′ ofsemiconductor device 10, which illustrates fuse 20, diodes 17′ and 19′,and Schottky diode 15′. As fuse 20 is intact, current flows fromterminal region end 22, through conductive region 26, to terminal regionend 24 (see FIG. 1).

[0048] Upon application of a programming current to fuse 20, asillustrated in FIG. 4, fuse 20 is preferably rendered discontinuousadjacent the interface between common well 14 and well 18 at surface 13,which interface is also referred to herein as a boundary or border.Accordingly, terminal region 24 of fuse 20, which comprises a secondportion 24′ of the “blown” fuse 20, does not overlap common well 14.Thus, second portion 24′ of fuse 20 is not part of a Schottky diode.FIG. 4A is a schematic representation of the open circuit 10′ ofsemiconductor device 10 that is created as fuse 20 is “blown.”

[0049] With continued reference to FIGS. 4 and 4A, as a current isapplied to contact 30, the current is conducted into common well 14through well 16 and, therefore, through diode 17′. As diode 19′, locatedat the p-n junction 19 between common well 14 and well 18, preventscurrent from flowing from common well 14 into well 18 and since noSchottky diode exists between common well 14 and second portion 24′ offuse 20, the current, at a normal operating voltage of semiconductordevice 10, will not flow into the outlet terminal region 24 of fuse 20.Thus, an open circuit has been created which conducts substantially nocurrent.

[0050] Turning to FIGS. 5 and 5A, if fuse 20 is blown such that both afirst portion 22′ thereof, which is in communication with well 18, and asecond portion 24′ thereof, which is in communication with well 16, bothinclude regions that partially overlap common well 14, Schottky diodes15 a′ and 15 b′ will result at the interfaces between first portion 22′and common well 14 and between second portion 24′ and common well 14.Fuse 20 may “blow” in this manner when too high a programming current isapplied thereto or if the volume of conductive material of narrowedregion 28 of central region 26 is not sufficiently less than the volumesof conductive material of both central region 26 and terminal region 24.As Schottky diodes 15 a′ and 15 b′ exist where first portion 22′ andsecond portion 24′, respectively, of fuse 20 contact common well 14, thevoltage across Schottky diode 15 b′ may be sufficient to reverse-biasSchottky diode 15 b′ during normal operation of semiconductor device 10.If Schottky diode 15 b′ becomes reverse-biased, Schottky diode 15 b′will “leak” current to terminal region 24. Thus, although fuse 20 hasbeen “blown,” circuit 10′ of semiconductor device 10 may continue toconduct current. The voltage at which Schottky diode 15 b′ becomesreverse-biased depends upon the dopant and the dopant concentrationemployed to form common well 14.

[0051] Referring to FIG. 2, an alternative embodiment of a semiconductordevice 110, including a fuse 120 according to the present invention, isillustrated. Semiconductor device 110 includes a semiconductor substrate112 with a common well 114 disposed adjacent a surface 113 thereof. Atleast two separate, spaced-apart wells 116 and 118 are disposed adjacentsurface 113 and within or adjacent common well 114. A portion of surface113 of semiconductor substrate 112 that includes wells 116 and 118 andthe portion of common well 114 disposed between wells 116 and 118 isexposed through a field oxide 111 layer of semiconductor device 110. Anohmic contact 129 is also exposed through field oxide 111 and isdisposed in contact with common well 114.

[0052] A fuse 120 is disposed adjacent semiconductor substrate 112 andincludes at least two terminal regions 122 and 124, which are alsoreferred to herein as second regions, which communicate with wells 116and 118, respectively, and a central region 126, which is also referredto herein as a conductive region or as a first region. Central region126 is disposed between terminal regions 122 and 124 and adjacent theportion of common well 114 disposed between wells 116 and 118. Anarrowed region 128 of fuse 120 is disposed between central region 126and terminal region 124, the outlet terminal of fuse 120. Narrowedregion 128 is also disposed adjacent the interface between common well114 and well 118 at surface 113. Narrowed region 128 preferably has asmaller volume of conductive material than terminal regions 122 and 124and than central region 126.

[0053] Contacts 130 a, 130 b, and 132 may be disposed in communicationwith ohmic contact 129, well 116, and well 118, respectively. Contacts130 a and 130 b preferably both communicate with a current source.Terminal region 122 of fuse 120 communicates with contact 130 b.Terminal region 124 of fuse 120 communicates with contact 132.

[0054] Semiconductor substrate 112 may comprise a semiconductor wafer ora layer of semiconductor material disposed on an insulator, such as aSOG structure, a SOC structure, a SOS structure, or another SOIstructure. Semiconductor substrate 112 has preferably been lightly dopedwith a p-type dopant and, therefore, has a p-type conductivity.

[0055] Common well 114 has a first conductivity type, while wells 116and 118 have a second conductivity type, which is opposite the firstconductivity type. Preferably, common well 114 has an n-typeconductivity and is, therefore, an n-well. The second conductivity typeof wells 116 and 118 is preferably a p-type conductivity. Thus, wells116 and 118 are preferably p-wells. The dopant concentration of wells116 and 118 is preferably greater than the dopant concentration ofcommon well 114. Thus, common well 114 may be lightly doped, while wells116 and 118 may be heavily doped. Ohmic contact 129 preferably comprisesa well of semiconductor material having a greater concentration of thefirst conductivity type than common well 114.

[0056] Fuse 120 comprises metal silicide. Exemplary metal silicides thatmay be employed in fuse 120 include, without limitation, titaniumsilicide, tantalum silicide, tungsten silicide, molybdenum silicide,cobalt silicide, lead silicide, and platinum silicide. Preferably, uponthe application of a programming current, the metal silicide of fuse 120agglomerates, or “balls up,” and thereby becomes discontinuous. Suchagglomeration of the metal silicide of fuse 120 may prevent damage toregions of semiconductor device 110 or structures thereof that areproximate fuse 120 as fuse 120 is programmed.

[0057] Referring again to FIG. 1B, as with the previously describedembodiment, semiconductor device 110 includes diodes 17′ and 19′ at thep-n junctions 117 and 119 between well 116 and common well 114 andbetween well 118 and common well 114, respectively. As wells 116 and 118each preferably comprise a p-type semiconductor material and common well114 preferably comprises an n-type semiconductor material, diodes 17′and 19′ prevent current from traveling into wells 116 and 118 fromcommon well 114. A Schottky diode 15′ exists between central region 126of fuse 120 and the adjacent common well 114. Schottky diode 15′, whileforward-biased, prevents current from traveling from common well 114into central region 126 of fuse 120. As is known in the art, however, ata certain voltage, such as the normal operating voltage of semiconductordevice 110, Schottky diode 15′ may become reverse-biased. If Schottkydiode 15′ becomes reverse-biased, current will flow from common well 114into central region 126 of fuse 120. The circuit of semiconductor device110 is similar to that illustrated in FIG. 1B.

[0058]FIG. 3 illustrates another embodiment of a semiconductor device210, which includes a fuse 220 according to the present invention.Semiconductor device 210 includes a semiconductor substrate 212 with afield oxide layer 211 disposed thereon. A region of semiconductorsubstrate 212, which is exposed through field oxide 211, includes acommon well 214 of a first conductivity type and another well 218 of asecond conductivity type, which is opposite the first conductivity type.Well 218 is disposed within or adjacent common well 214. Both well 218and a portion of common well 214 are disposed adjacent a surface 213 ofsemiconductor substrate 212 and exposed through field oxide 211. Anotherwell of a first conductivity type, which comprises an ohmic contact 229,is disposed within or adjacent common well 214, adjacent surface 213,and is exposed through field oxide 211. Fuse 220 is disposed adjacent atleast common well 214 and well 218. A terminal region 224, which is alsoreferred to herein as a second region, of fuse 220 is disposed adjacentwell 218, while a conductive region 226, which is also referred toherein as a first region, of fuse 220 may be disposed in communicationwith the portion of common well 214 disposed adjacent well 218.Conductive region 226 and terminal region 224 communicate with anarrowed region 228 of fuse 220 disposed therebetween and adjacent theinterface between common well 214 and well 218 at surface 213. Narrowedregion 228 preferably has a smaller volume of conductive material thaneither conductive region 226 or terminal region 224.

[0059] Preferably, semiconductor substrate 212 comprises a wafer ofsemiconductor material or a layer of semiconductor material disposed onan insulator structure, such as a SOG structure, a SOC structure, a SOSstructure, or another SOI structure. Semiconductor substrate 212 ispreferably lightly doped to have a p-type conductivity.

[0060] The first conductivity type of common well 214 is preferably ann-type conductivity. Thus, common well 214 is preferably an n-well.Since well 218 comprises a semiconductor material having a secondconductivity type, well 218 preferably comprises semiconductor materialhaving a p-type conductivity. The concentration of p-type dopant in thesemiconductor material of well 218 preferably exceeds the concentrationof n-type dopant in the semiconductor material of common well 214.Accordingly, a diode 219′ (FIG. 3A) exists at the p-n junction 219between well 218 and common well 214. Due to the respective conductivitytypes of common well 214 and well 218, diode 219′ restricts electricalcurrent from flowing from common well 214 into well 218.

[0061] Fuse 220 comprises metal silicide. Exemplary metal silicides thatmay be employed in fuse 220 include, without limitation, titaniumsilicide, tantalum silicide, tungsten silicide, molybdenum silicide,cobalt silicide, lead silicide, and platinum silicide. Preferably, uponthe application of a programming current, the metal silicide of fuse 220agglomerates, or “balls up,” and thereby becomes discontinuous. Suchagglomeration of the metal silicide of fuse 220 may prevent damage toregions of semiconductor device 210 or structures thereof that areproximate fuse 220 as fuse 220 is programmed.

[0062] As conductive region 226 of fuse 220 is disposed adjacent thepreferably n-type common well 214, a Schottky diode 215′ (see FIG. 3A)is created at the interface between conductive region 226 and commonwell 214 While a forward-biased Schottky diode 215′ tends to preventcurrent from flowing from common well 214 into conductive region 226 offuse 220, if a sufficient voltage, such as the normal operating voltageof semiconductor device 210, is applied across Schottky diode 215′, thenSchottky diode 215′ will become reverse-biased and, therefore, permitcurrent to flow from common well 214 into conductive region 226 of fuse220. When Schottky diode 215′ is reverse-biased, however, current willnot readily flow from conductive region 226 into common well 214.

[0063] Ohmic contact 229 preferably comprises semiconductive material ofthe same conductivity type as that of common well 214. Thesemiconductive material of ohmic contact 229 may include a higherconcentration of dopant than the semiconductive material of common well214.

[0064] A first contact 230 may be disposed in communication withconductive region 226 of fuse 220. First contact 230 preferablycommunicates with a current source. A second contact 232 may be disposedin communication with ohmic contact 229.

[0065]FIG. 3A schematically illustrates a circuit 210′ of semiconductordevice 210. While fuse 220 remains intact, as a current is applied toconductive region 226 through first contact 230, the current may betransmitted into common well 214 by means of either diode 219′ orSchottky diode 215′. The current is then conducted through ohmic contact229 and, thus, to second contact 232.

[0066] Turning now to FIGS. 3B and 3C, upon applying at least aprogramming current to fuse 220, narrowed region 228 thereof willpreferably be rendered discontinuous. Accordingly, in order for currentto be conducted to common well 214, the current must past throughSchottky diode 215′. If, however, a sufficient voltage is applied acrossSchottky diode 215′, such as occurs during the course of normaloperation of semiconductor device 210, then Schottky diode 215′ willbecome reverse-biased and, therefore, will no longer permit the flow ofcurrent from conductive region 226 into common well 214.

[0067] FIGS. 6-12 illustrate an exemplary method of fabricatingconductivity doped wells and field isolation regions, such as fieldoxide regions or layers, on the semiconductor substrate illustrated inFIG. 2. The illustrated method includes the process flow typicallyemployed for fabricating a basic CMOS inverter. Accordingly, portions ofthe fabrication process of the present invention may be conductedsubstantially simultaneously with corresponding steps of known CMOSinverter fabrication processes or with processes for fabricating othersemiconductor device structures. It will be understood, however, bythose skilled in the art, that other semiconductor fuses could be formedby slight modifications to the described method, such as by substitutingdopants of an opposite polarity for those illustrated.

[0068] As shown in FIG. 6, a semiconductor substrate 12 is firstprovided. Semiconductor substrate 12 may comprise any material andsurface suitable for device formation, such as a semiconductor wafer(e.g., a silicon wafer), a SOI structure, a SOG structure, a SOCstructure, or a SOS structure. Semiconductor substrate 12 may be dopedand/or include an epitaxial layer. Preferably, semiconductor substrate12 is a silicon wafer that has been lightly doped with a p-type dopantof a type known in the art and by known processes.

[0069] With continued reference to FIG. 6, a mask 40 may be disposedover an active surface 13 of semiconductor substrate 12. Mask 40preferably includes apertures 41 therethrough, positioned to exposeregions of semiconductor substrate 12 where the fabrication of commonwells 14 (see FIG. 1) is desired. Mask 40 and the apertures 41 thereofmay be fabricated by any known, suitable process. Preferably, mask 40comprises a photomask and is, therefore, fabricated by disposing aquantity of photoresist onto surface 13 of semiconductor substrate 12,exposing and developing selected regions of the photoresist, andremoving any undeveloped photoresist from semiconductor device 10.

[0070] Referring to FIG. 7, a common well 14 of a first conductivitytype may be formed adjacent surface 13 of semiconductor substrate 12 byany suitable process known in the art, such as by diffusion orimplantation. Common well 14 may be formed in semiconductor substrate 12by a blanket implant of a conductivity dopant, as known in the art. Theconductivity dopant may be implanted into regions of semiconductorsubstrate 12 that are exposed through apertures 41 of mask 40 (see FIG.6). Common well 14 is preferably lightly doped (i.e., implanted with arelatively low concentration of conductivity dopant). The dopant ispreferably an n-type conductivity dopant. Accordingly, common well 14preferably includes semiconductor material of an n-type conductivity andis, therefore, an n-well. Mask 40 may be removed by any suitable processknown in the art.

[0071] With reference to FIGS. 8-10, a process of fabricating fieldisolation regions, such as field oxide 11, is illustrated. As shown inFIG. 8, another mask 42, including apertures 43 therethrough, may bedisposed adjacent surface 13 of semiconductor substrate 12. Any suitableprocess known in the art may be employed to dispose mask 42 ontosemiconductor substrate 12. Preferably, mask 42 comprises a photomaskand, therefore, may be disposed adjacent surface 13 by disposing aquantity of photoresist to adjacent surface 13, exposing and developingselected regions of the photoresist, and removing any undevelopedphotoresist from surface 13. Alternatively, a so-called hard mask may beemployed as mask 42. Preferably, apertures 43 of mask 42 are alignableover regions of semiconductor substrate 12 where the fabrication of afield isolation region, such as a field oxide 11 (see FIG. 10), isdesired.

[0072] Referring now to FIG. 9, regions of semiconductor substrate 12that are exposed through apertures 43 of mask 42 may be removed by knownprocesses, such as by the use of an etchant of the material ofsemiconductor substrate 12, to define trenches 11 within semiconductorsubstrate 12.

[0073] Turning now to FIG. 10, an insulative material, such as a siliconoxide or a glass (e.g., borophosphosilicate glass (“BPSG”),phosphosilicate glass (“PSG”), or borosilicate glass (“BSG”)), may bedisposed within trenches 11′. Known processes may be employed to disposeinsulative material within trenches 11′, such as chemical vapordeposition of a silicon oxide or glass or by spin-on-glass (“SOG”)processes. The insulative material within trenches 11′ is planarizedrelative to surface 13 of semiconductor substrate 12 by known processes,such as by known chemical-mechanical planarization (“CMP”) processes.Thus, trenches 11′ and the insulative material therein comprise regionsof field oxide 11 that do not protrude significantly above surface 13.This type of field oxide 11 region is typically referred to as a shallowtrench isolation (“STI”) field oxide.

[0074] Referring now to FIG. 11, the fabrication of two spaced-apartwells 16 and 18, which are also referred to herein as second wells,adjacent or within common well 14, is illustrated. Wells 16 and 18preferably comprise semiconductor material of a second conductivitytype. Wells 16 and 18 may be formed by any suitable, known process, suchas by disposing a mask 44 adjacent regions of semiconductor substrate 12which are not to be doped to have the second type of conductivity.Regions of semiconductor substrate 12 that are to be doped to have thesecond conductivity type are exposed through apertures 45 of mask 44.Preferably, mask 44 comprises a photomask, which may be fabricated bydisposing a photoresist over semiconductor substrate 12, exposing anddeveloping selected regions of the photoresist, and removing anyundeveloped photoresist from regions of semiconductor substrate 12 thatare to be doped. These regions of semiconductor substrate 12 that areexposed through apertures 45 may be doped by known processes to formwells 16 and 18. Preferably, wells 16 and 18 are heavily doped, relativeto the doping concentration of common well 14 (i.e., the dopantconcentrations of wells 16 and 18 exceeds the dopant concentration ofcommon well 14), with a p-type dopant. Thus, wells 16 and 18 have aconductivity type opposite the conductivity type of common well 14. Mask44 may then be removed by any suitable process known in the art.

[0075] Due to the opposite conductivity type of common well 14 from theconductivity type of wells 16 and 18, diodes 17′, 19′ (see, e.g., FIG.1B) are created at the p-n junctions 17, 19 between well 16 and commonwell 14 and between well 18 and common well 14, respectively. Theconcentrations and types of doping of wells 16 and 18 and of common well14 preferably impart diodes 17′ and 19′ with the desired conductivitycharacteristics, such as the direction in which the diodes, whenforward-biased, conduct current. The concentrations and types of dopingof wells 16 and 18 and of common well 14 also dictate, at least in part,the voltage or voltages at which diodes 17′ and 19′ will becomereverse-biased.

[0076] As illustrated in FIG. 12, yet another mask 46, includingapertures 47 therethrough, may be disposed over semiconductor substrate12. Apertures 47 preferably expose regions of semiconductor substrate 12that are to be more heavily doped with a dopant of a first conductivitytype than the concentration of dopant with which common well 14 wasdoped. Again, mask 46 and the apertures 47 therethrough may be definedby known processes and, preferably, are disposed and defined by knownphotomask processes. The regions of semiconductor substrate 12 that areexposed through apertures 47 may be doped with a dopant of a firstconductivity type and preferably with an n-type conductivity dopant, byknown processes. At least one of these regions of semiconductorsubstrate 12, which is disposed adjacent or otherwise in communicationwith common well 14, may be employed as an ohmic contact 29. Mask 46 maybe removed by any suitable process known in the art.

[0077] Referring now to FIGS. 13-18, another embodiment of a method offabricating conductivity doped wells and field isolation regions, suchas field oxides, on a semiconductor substrate is illustrated.

[0078] With reference to FIG. 13, a pad oxide layer 40′, which acts as amask and as a stress relief layer, may be formed over an active surface13 of semiconductor substrate 12 by any suitable process known in theart. Pad oxide layer 40′ may be thermally grown on semiconductorsubstrate 12 or deposited onto semiconductor substrate 12 by knownprocesses, such as chemical vapor deposition (“CVD”) oftetraethylorthosilicate (“TEOS”), or otherwise formed on semiconductorsubstrate 12 by known techniques. Layer 40′ may then be patterned byknown processes, such as by disposing a mask (e.g., a photomask) overlayer 40′ and removing material of layer 40′ through apertures of themask (e.g., by etching). Pad oxide layer 40′ preferably comprisessilicon oxide formed by thermal oxidation of a silicon semiconductorsubstrate 12.

[0079] With reference to FIG. 14, a common well 14′ of a firstconductivity type may be formed adjacent surface 13 of semiconductorsubstrate 12 by any suitable process known in the art, such as bydiffusion or implantation. Preferably, a mask 42′, such as a photomask,including apertures 43′ therethrough, is disposed over at least theexposed regions of semiconductor substrate 12 that are to be shieldedfrom the conductivity dopant. If a photomask is employed as mask 42′,photoresist may be disposed on semiconductor substrate 12, selectedregions of the photoresist exposed and developed to define mask 42′ andapertures 43′ therethrough, and any undeveloped photoresist removed frommask 42′ in order to form the same. Alternatively, a so-called hard maskmay be employed as mask 42′.

[0080] Common well 14′ may be formed in semiconductor substrate 12 by ablanket implant of a conductivity dopant, as known in the art. Theconductivity dopant may be implanted into regions of semiconductorsubstrate 12 that are exposed through apertures 43′ of mask 42′. Commonwell 14′ is preferably lightly doped (i.e., implanted with a relativelylow concentration of conductivity dopant). The dopant is preferably ann-type conductivity dopant. Accordingly, common well 14′ preferablyincludes semiconductive material of an n-type conductivity and is,therefore, an n-well. Mask 42′ may be removed from semiconductor device10 by any suitable process known in the art.

[0081]FIG. 15 illustrates the fabrication of two wells 16′ and 18′ ofsemiconductor material of a second conductivity type, which are alsoreferred to herein as second wells or as at least two spaced-apartwells. Wells 16′ and 18′ are formed adjacent surface 13 of semiconductorsubstrate 12 and within or adjacent common well 14′. Wells 16′ and 18′may be formed by any suitable process known in the art, such as bydisposing a mask 44′ over the regions of semiconductor substrate 12which are not to be doped to have the second conductivity type.Preferably, mask 44′ is formed by disposing a photoresist oversemiconductor substrate 12, exposing and developing selected regions ofthe photoresist, and removing undeveloped photoresist. Thus, mask 44′may comprise a photomask. Upon disposal of mask 44′ on semiconductorsubstrate 12, regions of semiconductor substrate 12 that are exposedthrough mask 44′ and through pad oxide layer 40′ may be doped by anysuitable doping process, such as by diffusion or implantation, to impartthese regions with a second conductivity type and, thereby, to formwells 16′ and 18′. Preferably, wells 16′ and 18′ are heavily doped,relative to the dopant concentration of common well 14′, with a p-typedopant. Thus, wells 16′ and 18′ have a conductivity type opposite theconductivity type of common well 14′. Mask 44′ may be removed by anysuitable process known in the art.

[0082] Due to the opposite conductivity type of common well 14′ from theconductivity type of wells 16′ and 18′, diodes are created at the p-njunctions 17′″, 19′″ between well 16′ and common well 14′ and betweenwell 18′ and common well 14′, respectively. The concentrations and typesof doping of wells 16′ and 18′ and of common well 14′ preferably impartthe diodes with the desired conductivity characteristics, such as thedirection in which the diodes, when forward-biased, conduct current. Theconcentrations and types of doping of wells 16′ and 18′ and of commonwell 14′ also dictate, at least in part, the voltage or voltages atwhich the diodes will become reverse-biased.

[0083] An ohmic contact 29′ (see FIG. 16) may also be formed adjacentcommon well 14′ by known processes, such as by the method disclosedherein in reference to FIG. 12.

[0084] As depicted in FIG. 16, a layer 46′ of silicon nitride or anothermasking material, such as a photomask, may be disposed oversemiconductor substrate 12 and pad oxide layer 40′. If layer 46′comprises silicon nitride, any suitable process known in the art, suchas a CVD process, can be employed to deposit layer 46′. As explainedbelow, layer 46′ may serve as a mask during the fabrication of fieldisolation regions, such as field oxide 11.

[0085] As shown in FIG. 17, regions of layer 46′ and pad oxide layer 40′that overlie the areas of semiconductor substrate 12 upon which thefabrication of field isolation regions, such as field oxide 11 (see FIG.18), is desired, may be removed. Any suitable patterning process knownin the art, such as the disposal of a mask 48′ (e.g., a photomask) andthe use of known etchants and etch processes, may be employed to removethese regions of layer 46′ and pad oxide layer 40′ and to, thereby,expose the regions of semiconductor substrate 12 upon which fabricationof field isolation regions is desired. For example, a quantity ofphotoresist can be spun onto an active surface of semiconductor device10, exposed, developed, and portions thereof removed to form mask 48′.Selected regions of layer 46′ and of pad oxide layer 40′ may be removedthrough mask 48′ by a known suitable etching process or processes. Mask48′ may be removed by any suitable process known in the art which doesnot attack the remaining regions of layer 46′, pad oxide layer 40′, orsemiconductor substrate 12.

[0086] Referring to FIG. 18, the field isolation regions, such as fieldoxide 11, may be formed on semiconductor substrate 12. The fieldisolation regions are preferably somewhat recessed insulative regions ofsemiconductor substrate 12, such as oxide regions, which may be formedby any suitable, known process. Preferably, the regions of semiconductorsubstrate 12 that are exposed through the remaining portions of layer46′ or pad oxide layer 40′ (see FIG. 17) are oxidized by known oxidationprocesses, such as by thermal oxidation techniques. Accordingly, layer46′ and pad oxide layer 40′ are employed as a mask during thefabrication of the field isolation regions. After the field isolationregions have been fabricated, layer 46′ and pad oxide layer 40′ may beremoved by any suitable process known in the art which does notsubstantially attack or remove semiconductor substrate 12 or the fieldisolation regions. For example, layer 46′ and pad oxide layer 40′ may beremoved by a wet etch process using hydrogen fluoride and/or phosphoricacid.

[0087] Once the conductively doped wells 14, 16, and 18 or 14′, 16′, and18′ and the field oxide 11 regions have been formed or fabricated onsemiconductor substrate 12, a metal silicide fuse 20 according to thepresent invention may be fabricated. Although FIGS. 19, 19A and 20illustrate the fabrication of fuse 20 on the semiconductor substrate ofFIG. 12, the fuse of the present invention may be fabricated upon oradjacent semiconductor devices having different configurations orfabricated by different processes.

[0088] With reference to FIG. 19, a layer 50 of metal silicide isdisposed at least over semiconductor substrate 12. Layer 50 may also bedisposed over field oxide 11. Layer 50 may be disposed by any suitable,known process, such as by chemical vapor depositing the metal silicideonto semiconductor device 10.

[0089] An exemplary tungsten silicide deposition process that may beemployed in the method of the present invention is disclosed in U.S.Pat. No. 5,231,056, which issued to Gurtej S. Sandhu on Jul. 27, 1993,the disclosure of which is hereby incorporated herein in its entirety bythis reference. If titanium silicide is employed as the metal silicideof layer 50, known titanium silicide deposition processes, such as thosedisclosed in U.S. Pat. Nos. 5,240,739, 5,278,100, and 5,376,405, each ofwhich issued to Trung T. Doan et al. on Aug. 31, 1993, Jan. 11, 1994,and Dec. 27, 1994, respectively, the disclosures of each of which arehereby incorporated herein by reference in their entireties, may beused.

[0090] Alternatively, as shown in FIG. 19A, adjacent layers 50 a and 50b, which comprise metal and silicon, respectively, may be disposed overa surface of semiconductor device 10 and annealed to form layer 50 ofmetal suicide (see FIG. 11). Layer 50 a of metal, which may comprise anymetal, such as titanium, tantalum, tungsten, molybdenum, cobalt, lead,nickel, or platinum, that will react with silicon to form a metalsilicide and which preferably comprises a refractory metal, may bedisposed on semiconductor device 10 by known processes, such as bychemical vapor deposition or physical vapor deposition (“PVD”) (e.g.,sputtering processes), depending, at least in part, upon the type ofmetal employed. Layer 50 b, which comprises silicon or polysilicon, maybe disposed on semiconductor device 10 by known processes, such as bychemical vapor deposition. Although a layer 50 b of silicon is shown tobe disposed over layer 50 a of metal, layer 50 b may be disposed underlayer 50 a. Alternatively, layer 50 a may be annealed to an upperportion of the adjacent semiconductor substrate 12, in which case itwould not be necessary to dispose layer 50 b comprising silicon adjacentlayer 50 a. When layer 50 comprises titanium or a titanium alloy, theannealing temperature may range from about 500° C. to about 800° C. andthe duration of time that layer 50 a and the adjacent silicon orpolysilicon are exposed to the annealing temperature may range fromabout 20 seconds to about 200 minutes.

[0091] As depicted in FIG. 20, layer 50 may be patterned by any suitableprocess known in the art to define fuse 20. While patterning layer 50 todefine fuse 20 therefrom, regions of layer 50 that overlie wells 16 and18 are preferably configured as terminal regions 22 and 24. The regionof layer 50 disposed between terminal regions 22 and 24, which region isdisposed directly adjacent the portion of common well 14 exposed tosurface 13 between wells 16 and 18, is configured as central region 26,which is also referred to herein as the conductive region, of fuse 20.Central region 26 is preferably narrower in width or has a smallermaterial volume than terminal regions 22 and 24. A narrowed, ornecked-down, region 28 of fuse 20, disposed between central region 26and terminal region 24, preferably has an even narrower width andsmaller material volume than central region 26.

[0092] Known processes, such as the disposal of a mask 52 over layer 50and the removal of portions of layer 50 that are exposed through mask52, may be employed to pattern layer 50. For example, mask 52 can bedisposed adjacent layer 50 by disposing a quantity of a photoresistmaterial adjacent layer 50 (e.g., by spin-on processes) and by exposingand developing selected regions of the photoresist material. Theportions of layer 50 that are exposed through mask 52 may be removed byany suitable etching process and with any suitable etchant of thematerial or materials of layer 50 to define fuse 20. Preferably, ifremoval of any structures or layers that underlie layer 50 is notdesired, the etching process and etchant will not substantially removethe material or materials of these structures or layers. Anisotropicetchants and etching processes are preferably employed to pattern layer50. If layer 50 is formed by annealing a layer 50 a (see FIG. 19A) ofmetal to an adjacent silicon or polysilicon structure or layer, themetal layer (and an adjacent silicon or polysilicon layer, if any) maybe patterned prior to annealing or layer 50 of metal silicide may bepatterned after layer 50 a of metal has been annealed to the adjacentsilicon or polysilicon.

[0093] Although the foregoing description contains many specifics andexamples, these should not be construed as limiting the scope of thepresent invention, but merely as providing illustrations of some of thepresently preferred embodiments. Similarly, other embodiments of theinvention may be devised which do not depart from the spirit or scope ofthe present invention. The scope of this invention is, therefore,indicated and limited only by the appended claims and their legalequivalents, rather than by the foregoing description. All additions,deletions and modifications to the invention as disclosed herein andwhich fall within the meaning of the claims are to be embraced withintheir scope.

What is claimed is:
 1. A semiconductor device comprising: a substrate including: a surface; at least one common well located adjacent to said surface and having a first conductivity type; and at least one second well adjacent to said surface, bordering said at least one common well, and having have a second conductivity type; and a fusible element including: a first region adjacent said at least one second well; a second region of reduced cross-sectional area positioned over a border between said at least one common well and said at least one second well; and a third region positioned adjacent said at least one common well.
 2. The semiconductor device of claim 1, wherein said first conductivity type and said second conductivity type are opposite one another.
 3. The semiconductor device of claim 1, wherein said first conductivity type comprises an n-type conductivity.
 4. The semiconductor device of claim 1, wherein said first conductivity type comprises a p-type conductivity.
 5. The semiconductor device of claim 1, comprising an interface between said at least one common well and said at least one second well.
 6. The semiconductor device of claim 5, wherein said interface comprises a diode.
 7. The semiconductor device of claim 6, wherein said diode prevents current from flowing from said at least one common well into said at least one second well.
 8. The semiconductor device of claim 1, wherein an interface between said third region of said fusible element and said at least one common well comprises a Schottky diode.
 9. The semiconductor device of claim 8, wherein said Schottky diode is reverse-biased.
 10. The semiconductor device of claim 9, wherein said Schottky diode permits electrical current to flow from said third region into said at least one common well.
 11. The semiconductor device of claim 1, further comprising an ohmic contact of said first conductivity type adjacent said at least one common well.
 12. The semiconductor device of claim 1, further comprising a first contact in communication with said third region of said fusible element.
 13. The semiconductor device of claim 12, further comprising a second contact in communication with said at least one common well.
 14. The semiconductor device of claim 1, further comprising at least one other second well of said second conductivity type positioned adjacent said at least one common well and spaced apart from said at least one second well.
 15. The semiconductor device of claim 14, wherein said fusible element comprises a fourth region adjacent said third region thereof, opposite from said second region, and in communication with said at least one other second well.
 16. The semiconductor device of claim 15, wherein said first conductivity type is an n-type conductivity and said second conductivity type is a p-type conductivity.
 17. The semiconductor device of claim 16, wherein a first interface between said at least one second well and said at least one common well comprises a first diode and a second interface between said at least one other second well and said at least one common well comprises a second diode.
 18. The semiconductor device of claim 17, wherein said first and second diodes prevent current from flowing from said at least one common well respectively into said at least one second well and said at least one other second well under a normal operating voltage of the semiconductor device.
 19. The semiconductor device of claim 15, further comprising an ohmic contact of said first conductivity type in communication with said at least one common well.
 20. The semiconductor device of claim 15, further comprising contacts in communication with each of said at least one second well and said at least one other second well.
 21. The semiconductor device of claim 1, wherein said fusible element comprises a metal silicide.
 22. The semiconductor device of claim 21, wherein said metal silicide comprises a refractory metal silicide.
 23. The semiconductor device of claim 21, wherein said metal silicide comprises at least one of titanium silicide, tantalum silicide, tungsten silicide, cobalt silicide, molybdenum silicide, lead silicide, nickel silicide, and platinum silicide.
 24. The semiconductor device of claim 1, wherein said second region of said fusible element comprises a smaller volume of material than said first region and than said third region.
 25. The semiconductor device of claim 1, wherein said second region of said fusible element is narrower than said first region and than said third region.
 26. A semiconductor device, comprising: a semiconductor substrate including: a surface; at least one common well adjacent to said surface and having a first conductivity type; and at least two second wells adjacent to both said surface and said at least one common well and spaced apart from one another, each of said at least two second wells having a second conductivity type; and at least one fusible element positioned adjacent said surface of said semiconductor substrate, said at least one fusible element including: at least two terminal regions, each of which is positioned over and communicates with a corresponding second well of said at least two second wells; a narrowed region adjacent an interface between at least one second well of said at least two second wells and said at least one common well; and a conductive region positioned over and in communication with said at least one common well.
 27. The semiconductor device of claim 26, wherein said narrowed region of said at least one fusible element comprises a smaller volume of material than said conductive region and than reach said terminal region.
 28. The semiconductor device of claim 26, wherein said first conductivity type comprises an n-type conductivity.
 29. The semiconductor device of claim 26, wherein said second conductivity type comprises a p-type conductivity.
 30. The semiconductor device of claim 26, wherein interfaces between said at least one common well and each second well of said at least two second wells comprise diodes.
 31. The semiconductor device of claim 30, wherein said diodes substantially prevent electrical current from flowing from said at least one common well into said at least two second wells under a normal operating voltage of the semiconductor device.
 32. The semiconductor device of claim 26, wherein an interface between said conductive region of said at least one fusible element and said at least one common well comprises a Schottky diode.
 33. The semiconductor device of claim 32, wherein said Schottky diode is reverse-biased.
 34. The semiconductor device of claim 33, wherein said Schottky diode permits electrical current to flow from said conductive region of said at least one fusible element into said at least one common well.
 35. The semiconductor device of claim 26, further comprising an ohmic contact of said first conductivity type disposed adjacent said at least one common well.
 36. The semiconductor device of claim 26, further comprising contacts for each of said conductive region of said at least one fusible element and for said at least one common well.
 37. The semiconductor device of claim 26, wherein said at least one fusible element includes a second terminal region adjacent said conductive region thereof and in communication with the other second well of said at least two second wells.
 38. The semiconductor device of claim 37, wherein said first conductivity type is an n-type conductivity and said second conductivity type is a p-type conductivity.
 39. The semiconductor device of claim 26, wherein said at least one fusible element comprises a metal silicide.
 40. The semiconductor device of claim 39, wherein said metal silicide comprises a refractory metal silicide.
 41. The semiconductor device of claim 39, wherein said metal silicide comprises at least one of titanium silicide, tantalum suicide, tungsten silicide, cobalt silicide, molybdenum silicide, lead silicide, nickel silicide, and platinum silicide. 